Super alloys are a broad range of nickel, iron, and cobalt base alloys developed specifically for applications demanding exceptional mechanical and chemical properties at elevated temperatures. The classic use for these alloys is in the hot end of aircraft engines and land based turbines. Almost every metallurgical change made to improve the high temperature properties makes it more difficult to machine these alloys.
As high temperature strength is increased, the alloys become harder and stiffer at the cutting temperature. It results in increased cutting forces and increased wear on the cutting edge during machining.
Because stronger materials generate more heat during chip formation and because the thermal heat conductivity of these alloys is relatively low, very high cutting temperatures are generated, this also contribute to an increased wear of the cutting edge.
To make matters even worse, as the alloys are heat treated to modify the as cast or solution treated properties, abrasive carbide precipitates or other second phase particles often form. These particles do also cause rapid wear of the cutting edge.
EP 1174528 provides a multilayer-coated cutting tool. The first hard coating film is formed on the substrate and a second hard coating film formed on the first hard coating film. The first hard coating film comprises one or more of Ti, Al, and Cr, and one or more of N, B, C, and O. The second hard coating film comprises Si, and one or more metallic elements selected from the group consisting of metallic elements of Groups 4a, 5a and 6a of the Periodic Table and Al, and one or more non-metallic elements selected from the group consisting of N, B, C, and O.
WO 2006/118513 relates to a cutting tool insert, solid end mill, or drill, comprising a substrate and a coating. The coating is composed of a cubic C-(Me, Si) N-phase without coexisting amorphous phase. It is deposited by arc evaporation.
EP 1736565 relates to a cutting tool insert, solid end mill, or drill, comprising a substrate and a coating. The coating is composed of one or more layers of refractory compounds of which at least one layer comprises a cubic (Me,Si)X phase, where Me is one or more of the elements Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and Al, and X is one or more of the elements N, C, O or B. The ratio R=(at-% X)/(at-% Me) of the c-MeSiX phase is between 0.5 and 1.0 and X contains less than 30 at-% of O+B.
US 2005/0019612 relates to a coated cutting tool made of cemented carbide with a hard coating layer, wherein (a) a crystal orientation hysteresis layer which consists of a carbonitride compound layer and (b) a hard coating layer which consists of a layer of nitride compound and has a well defined crystal orientation and/or degree of crystallinity are formed on the surface of a cemented carbide substrate, preferably on the surface of a tungsten carbide based cemented carbide or titanium carbonitride based cermet by physical vapor deposition, wherein the crystal orientation hysteresis layer is deposited between the surface of a cemented carbide substrate and the hard coating layer.
What is needed is a coated cemented carbide for fine wet turning of super alloys with improved wear resistance. The invention is directed to these, as well as other, important needs.